Water Knowledge

How to Read Your Water Test Report: A Guide to Understanding the Numbers

You took the crucial step of getting your water professionally tested. Now, a report has arrived, and it looks less like a simple answer and more like a chemistry exam. It’s a page filled with acronyms, numbers, and technical terms that can feel intimidating. But this report is the key to understanding your water, and learning to decode it is one of the most empowering things you can do as a homeowner.

Think of this guide as your personal translator. We will break down the essential terminology, walk through the common sections of a water test report, and help you understand what the results mean for your home and family. Your report isn’t a final grade; it’s a detailed roadmap, and by the end of this article, you’ll know how to read it.

Chapter 1: Decoding the Language: Units and Acronyms

Before looking at the numbers, you need to understand the language they’re written in. The units of measurement tell you the concentration of a substance in your water.

  • mg/L (Milligrams per Liter) and ppm (parts per million): These two units are essentially interchangeable for water. They are the most common units for minerals like calcium, magnesium, and iron.

    Analogy: One part per million (ppm) is equivalent to one drop of ink in a 50-liter car gas tank.

  • µg/L (Micrograms per Liter) and ppb (parts per billion): These units are also interchangeable and are 1,000 times smaller than ppm. They are used for highly toxic substances that are a health concern even at trace levels, such as lead and arsenic.

    Analogy: One part per billion (ppb) is equivalent to one drop of ink in a large swimming pool.

  • GPG (Grains Per Gallon): This unit is used almost exclusively for measuring water hardness. It’s an industry standard for water softeners. If your report uses mg/L or ppm for hardness, you can convert it: 1 GPG = 17.1 mg/L.

  • MCL (Maximum Contaminant Level): This is a critical acronym set by the U.S. Environmental Protection Agency (EPA). The MCL is the highest level of a contaminant that is allowed in public drinking water. It is an enforceable standard and your most important benchmark for health-related contaminants.

  • Action Level (AL): This is slightly different from an MCL. An Action Level is the concentration of a contaminant which, if exceeded, triggers treatment or other requirements that a water system must follow. It is most commonly used for Lead and Copper.

Chapter 2: A Guided Tour of Your Water Report

Most lab reports are organized into categories. While the layout may vary, the information is generally grouped by the type of analysis performed.

Section 1: Physical Properties

This section describes the aesthetic and functional characteristics of your water.

  • pH: A measure of acidity or alkalinity on a scale of 0-14. Water between 6.5 and 8.5 is considered ideal. Below 6.5, water is acidic and can corrode pipes. Above 8.5, it is alkaline and can cause scale or taste bitter.
  • Hardness: The concentration of calcium and magnesium. It’s the source of limescale. Any result over 7 GPG (or 120 mg/L) is considered significantly hard and will likely cause issues with appliances and soap scum.
  • Total Dissolved Solids (TDS): A measure of all dissolved substances in the water. High TDS can affect taste, but it is not necessarily a health indicator on its own.

Section 2: Inorganic Contaminants (Metals and Nutrients)

This is where you’ll find results for many of the key health-related contaminants.

  • Lead & Copper: Compare your result directly to the EPA’s Action Levels (Lead AL = 15 ppb, Copper AL = 1,300 ppb). Any detectable lead is a concern for families with children.
  • Arsenic: Compare your result to the EPA’s MCL of 10 ppb. Because it is a carcinogen, the goal is to have this number as close to zero as possible.
  • Nitrate: Compare your result to the EPA’s MCL of 10 ppm. This is the critical limit to prevent “blue baby syndrome” in infants.
  • Iron & Manganese: These are typically aesthetic issues. Iron levels above 0.3 ppm (or 300 ppb) will likely cause red/orange staining. Manganese above 0.05 ppm (or 50 ppb) can cause blackish stains.

Section 3: Microbiological Results

This section is the most important for well owners. The results are usually not given in numbers.

  • Total Coliforms: The result will be either “Absent” (or “Not Detected”) or “Present” (or “Detected”). “Absent” is good. “Present” indicates that a pathway for contamination exists in your well system and it needs to be inspected and disinfected.
  • E. coli: The result will also be “Absent” or “Present”. If E. coli is “Present”, your water is considered unsafe to drink and requires immediate action, like boiling your water or switching to bottled water until the system is treated and re-tested.

Chapter 3: Context Is Everything: What the Numbers Mean for You

Once you’ve decoded the terms, you need to put the numbers in context. Ask yourself three questions as you review your report:

  1. Is There a Health Concern? Compare your results for lead, arsenic, nitrates, and bacteria directly against the EPA’s MCLs or Action Levels. Any result exceeding these official limits is a clear sign that a treatment solution is needed for health protection.

  2. Will My Home Be Damaged? Look at the “Plumbing Health Trio”—pH, hardness, and alkalinity. Is your pH low enough to cause corrosion? Is your hardness high enough to destroy your water heater with scale? These numbers predict the long-term health of your pipes and appliances.

  3. Will I Have Nuisance Issues? Look at the results for iron, manganese, and TDS. Even if they are well below the health limits, are they high enough to cause the stains and bad tastes you’ve been noticing? This helps you target solutions for a better quality of life.

Conclusion: Your Report Is a Roadmap, Not a Final Destination

A water test report transforms you from a homeowner with a problem into a homeowner with a plan. It takes away the mystery and replaces it with facts. With this newfound understanding of the language and layout of your results, you are now equipped to make clear, informed decisions. You can confidently seek out the right solutions for the specific issues your water has, ensuring the health, safety, and longevity of your home and family.